1. Field of the Invention
The present invention relates to a method of and apparatus for the quenching and scrubbing of gases. More particularly, the present invention relates to a method of and apparatus for the cooling of hot gas and removal of condensables by counter-current liquid contact between a gas and a cooling/scrubbing solution. The model system is the quenching and scrubbing of nitrogen gas using ethylene glycol.
2. Background
The cooling and purification of gases is important because large quantities of inert gases are used in many commercial processes. One particular such use is in the production of polyethylene terephthalate (PET) polymer. Specifically, inert gases are used during the polymerization reaction of PET to develop molecular weight by removing unwanted byproducts and excess reactants from the polymer resin such as ethylene glycol, acetaldehyde, and water. Hence, the presence of pure inert gases facilitates the solid state polymerization reaction. A complete description of this particular gas cleaning application is -found in several references including U.S. Pat. Nos. 5,434,239; 4,263,425; 4,356,299; 4,340,721 and 4,230,819, all herein incorporated by reference.
Moreover, since effective polymerization depends on the ability of the gas to strip contaminants which in turn depends on the purity of the gas, the polymerization reaction chamber requires continual replenishment of clean gas. Once the gas leaves the polymerization chamber, however, it contains the above mentioned contaminants. Before further use in the polymerization reaction therefore, the gas itself must be cleaned of contaminants. Such recycling reduces the cost associated with supplying a continuous stream of virgin gas to the polymerization reaction chamber while maintaining polymer line throughput.
Cleaning usually consists of cooling the gas by direct contact with a cool liquid so as to cool and condense out contaminants. These steps are respectively referred to as quenching and scrubbing. A typical gas stream exiting a polymer production apparatus is extremely hot, approximately 175.degree. C. It therefore initially requires extensive quenching to complete the recycle process. Only then does it undergo a scrubbing/absorption step where the majority of condensation of gas contaminants occurs.